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<正> 近交和选择是为配合杂交进行纯种猪群选育的基本手段。在育种猪群中,常因近交程度的增加而导致繁殖力(如每窝的活产仔数和断奶仔猪数)、生长速度和生存率的减退。不过在选择进程中还要求纯种猪群有一定程度的近交。这是因为:一方面近交具有暴露群体内有害隐性基因的作用,通过选择淘汰可改造净化群体的遗传素质;另一方面近交还可在每一群体中分别纯合不同位点的优良基因,通过杂交配合可进一步发挥近交和选择应产生的效应。本文试图应用北京花猪Ⅰ系的育种数据资料,分析研讨育种过程中近交和选择的相互关系。 相似文献
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近交可使基因趋于纯合,巩固有益性状;暴露不利性状,便于选留和淘汰。因而近交作为育种工作的重要手段,已被广泛应用。但是,由于近交会使牛的繁殖力、适应性、生活力等有不同程度的降低,且因近交使纯合体比率增加,杂合体比率减少,致杂合效应值降低,必然降低群体均值,导致生产性能的下降。奶牛产奶量为中等的遗传力,受近交影响比较敏感,但其影响程度如何,报道不多。本文对不同近交程度个体牛的产奶量进行了统计,以分析近亲繁殖对产奶量的影响,从而为在育种工作中确定适宜的近交程度提供依据。 相似文献
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分析群体近交程度是群体遗传学研究的基本内容．对指导动物育种和保种工作具有重要的意义。畜禽群体近交程度分析包括整理系谱资料、计算个体近交系数和群体平均近交系数、个体间亲缘系数和群体平均亲缘系数以及预测后代近交程度等内容．其核心内容是计算近交和亲缘系数、而计算近交和亲缘系数的方法目前主要有通径回路法与亲子协方差表法两种。相比之下以亲子协方差表法更适合一般系谱资料和容易计算机编程。本文围绕亲子协方差表法、在推导出亲子间近交和亲缘系数关系的基础上，采用先进的计算机语言研制了畜禽群体近交程度分析系统。１分… 相似文献
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旨在探讨高度近交陆川猪的遗传稳定性。本试验采集20头近交和6头非近交陆川猪的耳组织样品进行个体基因组重测序,通过扫描全基因组SNPs分析近交陆川猪群体的遗传多样性,并基于基因组纯合度挖掘近交陆川猪群体中特异的纯合区域（region of homozygosity,ROHs）及相关基因。结果表明,近交陆川猪群体的观察杂合度（0.373）小于期望杂合度（0.491）,推测其发生了选择或者近交;系统进化树和群体遗传结构分析发现,近交陆川猪群体在近交过程中分化成为两个近交家系,且230、236、239、132、130及126号个体亲缘关系最近;在近交群体中,基因组纯合度和基因组长纯合片段比例的均值分别为59.64%和0.12,都极显著高于非近交群体53.18%和0.05（P<0.01）,说明该近交陆川猪群体已达到高度近交;近交群体和非近交群体中分别有1 250和633个ROHs,重叠分析结果显示,特异存在于近交群体中的阳性纯合区域（positive region of homozygosity,pROHs）有224个,其中由于近交产生的纯合突变可能影响参与激素合成过程、胰液分泌、膜脂代谢过程、IgA产生的肠道免疫网络及纹肌细胞分化等相关的1 322个基因。结果提示,近交陆川猪群体的遗传多样性低、基因组纯合度高且已达到高度近交,说明该群体的遗传稳定性高。此外,近交陆川猪群体在近交过程中产生的纯合突变可能与机体的免疫、生长等生产性状相关。 相似文献
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《畜牧兽医学报》2020,(8)
旨在探讨高度近交陆川猪的遗传稳定性。本试验采集20头近交和6头非近交陆川猪的耳组织样品进行个体基因组重测序,通过扫描全基因组SNPs分析近交陆川猪群体的遗传多样性,并基于基因组纯合度挖掘近交陆川猪群体中特异的纯合区域(region of homozygosity, ROHs)及相关基因。结果表明,近交陆川猪群体的观察杂合度(0.373)小于期望杂合度(0.491),推测其发生了选择或者近交;系统进化树和群体遗传结构分析发现,近交陆川猪群体在近交过程中分化成为两个近交家系,且230、236、239、132、130及126号个体亲缘关系最近;在近交群体中,基因组纯合度和基因组长纯合片段比例的均值分别为59.64%和0.12,都极显著高于非近交群体53.18%和0.05(P0.01),说明该近交陆川猪群体已达到高度近交;近交群体和非近交群体中分别有1 250和633个ROHs,重叠分析结果显示,特异存在于近交群体中的阳性纯合区域(positive region of homozygosity, pROHs)有224个,其中由于近交产生的纯合突变可能影响参与激素合成过程、胰液分泌、膜脂代谢过程、IgA产生的肠道免疫网络及纹肌细胞分化等相关的1 322个基因。结果提示,近交陆川猪群体的遗传多样性低、基因组纯合度高且已达到高度近交,说明该群体的遗传稳定性高。此外,近交陆川猪群体在近交过程中产生的纯合突变可能与机体的免疫、生长等生产性状相关。 相似文献
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畜牧学上讲的“近交”是指双方到共同祖先的总代数不超过6代的个体间的互相交配。纵观家畜育种史,可以看到世界上几乎所有优良品种的培育过程中都不同程度地采用过近交。自从本世纪20年代,美国一些试验站开始系统进行猪的近交试验以来,近交在养猪业育种工作中得到了更为广泛的应用。但是长期以来,对于近交的作用究竟多大以及如何运用近交等等问题,曾出现过各种各样的看法及多次反复争论,人们有时把近交作为育种改良的灵丹妙药而争相采用,有时又将近交视为祸害而全盘否定。即使到了今天,人们对于近交的看法仍然是莫衷一是。究其原因, 相似文献
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对于东北半细毛羊种群的近交程度，近年来鲜有分析和研究。本文通过全面整理黑龙江省勃利地区东北半细毛种羊场自建场以来的留种与产仔资料，在理清系谱关系的基础上，对该场东北半细毛种羊场的近交程度作了系统分析，并探讨了引起近交程度变化的原因及其与保种措施的关系。 相似文献
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Selection of animals based on their BLUP evaluations from an animal model results in animals that are closely related which leads to increased rates of inbreeding. The tendency for higher inbreeding rates is greater at low heritability values. Several attempts have been made to reduce the impact of parent average breeding values from animals evaluations in order to reduce inbreeding while not sacrificing genetic response. A method that modifies the rules for forming the inverse of the additive genetic relationship matrix for use in best linear unbiased estimation of breeding values via an animal model was developed. This method and several others were compared analytically and empirically, from the perspective of partitioning the animal solutions into contributions from the data, from progeny, and from the parent average. The ratio of genetic progress to average level of inbreeding showed that the modified relationship matrix method was superior to the other methods. Similar results could be obtained by using artificially high heritability in a usual BLUP analysis. 相似文献
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Findings within the last 15 years emphasize the possible role of genomic imprinting for trait expression in livestock species. In genetic evaluation, genomically imprinted traits can be treated by models with two different breeding values per animal; one accounts for the paternal and the other for the maternal expression pattern. Relative weighting factors for these breeding values were derived by a generalized version of the discounted gene flow method, which was extended to a gametic level to account for parent‐of‐origin effects. The gametic approach proved also useful for calculating the expected increase in inbreeding induced by one round of selection and its dynamics over time. The gametic gene flow method was applied to a hypothetical pig breeding programme. Relative weighting factors were higher for the paternally inherited genetic effect even in female selection paths, but depend on the breeding scheme heavily. The maximum medium‐term increase in inbreeding due to selection exceeded the long‐term increase in a range of 20–100%. 相似文献
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Records from 7,200 separate closed herds with either 12 or 25 sows that were mated to either four or eight boars per year were simulated by computer. Effects of selection method, herd size, and contemporary group variability on average genetic change, genetic variance, and inbreeding over 10 yr of selection were analyzed for traits with heritabilities of .1, .3, and .6. Selection of replacement animals was on individual phenotype or BLUP of breeding value using a reduced animal model. For both of these selection methods, two culling schemes were imposed: 1) based only on involuntary culling because of losses due to conception rate and age and 2) when an available replacement animal was projected to be superior to an existing breeding animal in the herd in addition to the involuntary culling. The contemporary group standard deviation was set at either .1 or .5 of a phenotypic standard deviation. Selection with BLUP gave 72, 36, and 12% more genetic improvement for heritabilities of .1, .3, and .6, respectively, than selection on individual phenotype after 10 yr. However, inbreeding increased 20 to 52% more rapidly and there was a decrease in genetic variance. Culling based on Scheme 2 increased genetic improvement over Scheme 1 by about 75% with coincident increases in inbreeding level and decreases in genetic variance. The largest changes in inbreeding and genetic variance were associated with culling on BLUP. Culling when a superior animal was available with individual phenotype had little effect on inbreeding and genetic variance. Use of four boars rather than eight boars and 25 rather than 12 sows per herd increased genetic response. Use of four boars also increased inbreeding and decreased genetic variance. Genetic variance was higher in herds with 25 sows, but the size of the sow herd had little effect on inbreeding. Contemporary group variation influenced only the genetic response of individual phenotypic selection with culling. 相似文献
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By T. Oikawa K. Sato S. Takahashi 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》1999,116(6):467-473
The inbreeding coefficient (F) is used as a central parameter inferring a proportion of alleles identical by descent within an individual and by genetic variability within a population. The actual inbreeding coefficient varies around a central value, the inbreeding coefficient. C ockerham and W eir (1983) derived the method for computing the variance of inbreeding while reviewing several other methods. The variance of inbreeding in their report was considered to be of two components: one within population and the other between population of varied pedigrees. If pedigree is fixed, F is easily computed for an individual by the standard method (F alconer 1989). For domestic animals, pedigree information is usually available because it is requisite for a programme of genetic improvement. In this study, the variance of inbreeding coefficient was derived for an individual with a pedigree having a single path to a foundation animal. 相似文献
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The objective of this study was to analyze the development of inbreeding and estimate inbreeding depression in the Danish populations of 3 major meat type sheep breeds. The pedigrees contained 29,336 Texel, 22,838 Shropshire, and 11,487 Oxford Down. The rate of inbreeding was approximately 1% per generation for all breeds, but the rate of increase in co-ancestry was somewhat lower (0.45 to 0.71), indicating that more inbreeding has been accumulating than would be expected if mating was at random. Inbreeding depression for birth weight, ADG from birth until 2 mo, and litter size was estimated for all 3 breeds using a minimum of 15,000 records per trait and breed. All traits showed depression due to inbreeding of the animal itself. For most combinations of trait and breed, there was also a significant reduction of the phenotype due to inbreeding in the dam. The size of inbreeding depression was 1.2 to 2.6% of the mean, resulting in an increase in the inbreeding coefficient of the individual of 0.10, and estimates were similar for similar increases in maternal inbreeding. The rate of inbreeding in these breeds needs to be reduced in the future to avoid a further decline in birth weight, ADG, and litter size. 相似文献
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JB Siqueira RO Pinho SEF Guimarães T Miranda Neto JD Guimarães 《Reproduction in domestic animals》2010,45(6):1122-1125
This case study reported the presence of short tail sperm defect in the semen of three Nelore breed bulls. The sperm presented 0% of motility in the three animals evaluated and a total of 70%, 61% and 34% of pathologies of the intermediate piece of the tail respectively for animals 1, 2 and 3. It was identified that animals 2 and 3 had high degree of inbreeding, although no relationship was found with animal 1. Animal 2 was the only one that presented inbreeding coefficient (6.25%). His half‐sib (animal 3) and animal 1, from the same herd, had shown no inbreeding, showing that inheritance is not the only determinant factor for its incidence on Nelore males. 相似文献
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通过分组选配决策变量的提出,本文将家畜的分组过程和组间首次选配过程联立起来,建立了家畜分组选配的二次规划数学模型,实现了整个分组选配过程的最优化。应用该法制定民猪分组选配方案,所生后代近交系数期望值为0.07525,比采用聚类分析法分组,再用线性规划法进行组间选配的结果(0.0886)低15.07％。 相似文献
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在采用动物模型最佳线性无偏预测(BLUP) 方法对个体育种值进行估计的基础上, 模拟了在一个闭锁群体内连续对单个性状选择10个世代的情形, 并系统地比较了群体规模、公母比例和性状遗传力对选择所获得的遗传进展和群体近交系数变化的影响。结果表明, 扩大育种群规模不仅可以获得更大的持续进展, 同时还可有效缓解近交系数的过快上升; 育种群中公畜比例过低时, 不仅会降低遗传进展, 群体近交系数的上升速度也会加快, 实际中应保证育种群具有一定的规模和适宜的公母比例。对高遗传力性状进行选择时, 可望获得更大的遗传进展, 同时近交系数的上升速度也会快一些。 相似文献
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Although inbreeding (F) is a topic of major concern in animal breeding, estimates of inbreeding depression are usually obtained by modeling the overall F coefficient of each individual, without considering that the recessive (deleterious) genetic load of a given population may be unevenly distributed among the founder genomes. The founder-specific partial F coefficient is calculated as the identity-by-descent probability at any given autosomal locus related to a particular founder and allows a more detailed analysis of inbreeding depression on productive traits. Within this context, birth BW data from 2,459 Ripollesa lambs were analyzed under a hierarchical animal model without F-related covariates (model 0), with inbreeding depression modeled by the overall F coefficient (model F1), or by the partial F coefficient of 9 founders that made a relevant contribution to the population inbreeding (model F2). A straightforward empirical Bayes factor (BF) was developed for testing statistical relevance of each F-related covariate, in which greater-than-1 values favored the model including the covariate. The deviance information criterion (DIC) clearly supported model F1 (5,767.8) rather than model 0 (5,771.2), suggesting that inbreeding depression had a relevant influence on birth BW data. The linear effect of inbreeding depression was statistically relevant in model F1 (BF = 2.52 x 10(35)), with lamb birth BW declining by -13.6 g with each 1% F increase. The quadratic effect of inbreeding depression was almost null in model F1 (BF = 0.02), as suggested by the reduction in DIC (5,766.9) when this effect was removed from model F1. On the other hand, model F2 provided a similar DIC (5,767.9) value, with this parameter decreasing to 5,764.7 when nonrelevant founder-specific inbreeding depression effects were removed. Substantial heterogeneity in founder-specific inbreeding depression was reported by model F2, in which estimates for 4 of the 9 founders did not differ from zero (BF between 0.05 and 0.42), whereas 5 founders originated moderate (-8.2 g for each 1% F increase; BF = 1.42) to large inbreeding depression (-96.2 g for each 1% F increase; BF = 8.80 x 10(19)). The substantial variability between founder estimates suggested that inbreeding depression effects may mainly be due to a few alleles with major deleterious effects. These results contribute valuable information that should help to achieve more accurate management of inbreeding in the Ripollesa breed. 相似文献